Probably not your problem but it is a much better ground once you clean it up like that.
I can't imagine that the ground path between the battery and the alternator involves a chassis ground connection. Negative from the battery should be bolted somewhere on the engine, and the alternator frame ought to be bolted to a bracket also bolted to that engine.
Putting a multimeter between the battery negative terminal and the alternator frame would tell if there's excessive voltage drop in the ground path.